Magnetic and MO recording media are widely employed in various applications, particularly in the computer industry for data/information recording, storage, and retrieval purposes. A magnetic medium in, e.g., disk form, such as utilized in computer-related applications, comprises a non-magnetic substrate, for example, of glass, ceramic, glass-ceramic composite, polymer, metal or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Al—Mg), having at least one major surface on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. In the case of longitudinal type magnetic recording media, such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Ni—P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Cr—V), a longitudinally oriented magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon (C)-based material, such as diamond-like carbon (DLC), having good mechanical (i.e., tribological) and corrosion resistance properties. Perpendicular type magnetic recording media typically comprise, in sequence from the surface of a non-magnetic substrate, an underlayer of a magnetically soft material, at least one non-magnetic interlayer or intermediate layer, a vertically (i.e., perpendicularly) oriented recording layer of a magnetically hard material, and a protective overcoat layer.
A similar situation exists with magneto-optical (MO) media, wherein a layer stack is formed which comprises a reflective layer, typically of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more dielectric layers, and a protective overcoat layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
According to conventional manufacturing technology, a majority (if not all) of the above-described layers constituting stacked multi-layer longitudinal and perpendicular magnetic media, as well as MO recording media, are deposited by means of cathode sputtering processing. For example, the magnetic recording layers are typically fabricated by sputter depositing a Co-based alloy film, wherein the alloying elements are selected to promote desired magnetic and microstructural properties. In the case of longitudinal-type magnetic disk recording media, metallic and metalloidal elements, such as, for example, Cr, Pt, Ta, B, and combinations thereof, have been found to be effective. Similar alloying elements have been found to be useful in the case of perpendicular-type magnetic disk recording media, and in addition, reactive sputter deposition of the Co-based alloys in an oxygen (O2)-containing atmosphere has been found to be especially effective in controlling (i.e., limiting) exchange coupling between adjacent magnetic grains.
In a typical reactive sputtering process utilized for formation of perpendicular-type magnetic recording media, O2 gas is mixed with an inert sputtering gas, e.g., Ar, and is consumed by the depositing Co-based alloy magnetic film. Due to the high reactivity of O2 with metals, and since only partial oxidation of the depositing Co-based alloy magnetic film is desired, the degree of oxidation as a function of the location or position on the substrate (i.e., disk) surface tends to exhibit wide variation depending upon the process conditions, including, inter alia, O2 injection geometry, gas pumping (i.e., evacuation) geometry, gas flow rate, and film deposition rate.
FIG. 1 is a simplified, schematic, perspective view of a portion of an example of a one disk at-a-time sputtering apparatus 10 which may be utilized for sputter deposition of thin films as part of the manufacturing process of disk-shaped magnetic or MO recording media. As illustrated, apparatus 10 comprises: a vacuum chamber 1 equipped with an opening 2 at the bottom end thereof for connection to a pumping means for evacuating the interior of the chamber; at least one, preferably a pair of facing, circularly-shaped sputtering targets or sources 3A and 3B of conventional type, e.g., a pair of magnetron sputtering guns; a workpiece support or holder (not shown in the figure for illustrative clarity) for positioning a substrate/workpiece in the space between the pair of facing sputtering sources, illustratively a circular disk-shaped substrate 4 for a magnetic or MO recording medium, adapted for receipt of sputtered particle flux on the opposing surfaces thereof; and a gas injector 5 having a gas inlet portion 6 extending outside of chamber 1 for connection to a source of a process gas, and a gas outlet portion 7 within the chamber, for injecting the process gas, e.g., an inert gas such as Ar, Kr, etc., or a reactive gas such as N2, O2, etc., in the space between the facing pair of sputtering sources 3A and 3B. Illustratively, the gas injector 5 is “wishbone”-shaped, and comprises a linearly elongated, tubular inlet portion 6 having a first, gas inlet end, and a second end 7, with a pair of arcuately-shaped, tubular gas outlet portions 8A and 8B extending from the second end, comprising a plurality of spaced-apart, narrow diameter gas outlet orifices 9.
It has been determined that one-disk-at-a-time sputtering apparatus for the hard disk manufacturing industry, such as described above, employ gas injection systems with design criteria, e.g., geometries, which are poorly suited to the high film uniformity requirements of the hard disk industry, particularly with respect to the special problems presented by reactive sputtering in atmospheres containing O2 for formation of granular magnetic recording layers. For example, as the oxide content of granular magnetic films increases, the exchange coupling between adjacent magnetic grains decreases, the hysteresis slope decreases, and S* (a measure of the oxygen content) decreases.
More specifically, in the case of “top-center” O2/Ar injection, S* is highest at the bottom of the disks (i.e., at 180°), indicating that the bottom of the disks is oxide-poor, relative to the disk top and sides (i.e., 0, 90, and 270°). By contrast, in the case of “bottom-side” O2/Ar injection, S* is lowest, i.e., the oxide content is highest, at the 90° position, corresponding to the region of the disk directly above the O2/Ar injection port. However, variation, e.g., asymmetry, of the oxide content of the deposited magnetic films, as inferred from the values of the parameter S*, can be correlated with the O2/Ar injection geometry of the sputtering apparatus. In general, the oxide content is highest in the region of the disk surface which is closest to the point of O2/Ar injection. For the same sputtering chamber and pumping (evacuation) hardware, disks can be manufactured in which the magnetic recording layer is oxide rich at the top, bottom, or side(s), depending upon the geometry of the O2/Ar injection system, suggesting that the variation in oxide content of the magnetic recording layer (as reflected in the value of S*) can be reduced by proper design of the injection geometry/system.
FIG. 2 is a simplified, schematic, view of a portion (i.e., a center sectional view) of another example of a one at-a-time sputtering apparatus 20 which may be utilized for sputter deposition of thin films as part of the manufacturing process of disk-shaped magnetic and MO recording media. As illustrated, sputtering apparatus 20 comprises a vacuum chamber 11 equipped with a vertically movable workpiece/substrate mount or holder 12 for positioning a circular disk-shaped media substrate 4 in spaced opposition to a circularly-shaped sputtering target or source 13 of conventional type, e.g., a magnetron sputtering gun, for receipt of sputtered particle flux on a first, facing surface thereof. Chamber 11 typically includes another, similarly configured, circularly-shaped sputtering target or source (not shown in FIG. 2) positioned in spaced opposition to a second, opposing surface of substrate 4 for sputter deposition thereon. As shown in the figure, chamber 11 is provided with a pair of channels 13A and 13B which extend through the chamber base 12 at opposite ends thereof for supplying process gas(es) to the interior space of the chamber. Each of the channels 13A and 13B includes a respective branch portion 14A and 14B terminating at gas injection ports or orifices 15A and 15B formed in respective interior wall portions 16A and 16B of chamber 11 for supplying process gas to the lower portion of the chamber, as well as respective elongated, upwardly extending branches 17A and 17B respectively terminating in side gas injection ports or orifices 18A and 18B and top gas injection ports or orifices 19A and 19B for supplying process gas(es) to the side and upper portions of chamber 11. The process gas(es) supplied to the interior of chamber 11 is (are) evacuated via outlets at the lower portion of the chamber (not shown in the figure for illustrative simplicity).
According to this arrangement, control of the process gas pressure distribution within chamber 11 is possible only by closing or opening selected ones of gas injection ports or orifices 13A, 13B, 18A, 18B, 19A, and 19B. For example, if the bottom and side gas injection ports or orifices 13A, 13B, 18A, and 18B are closed (e.g., plugged), the process gas is injected only via the top gas injection ports or orifices 19A and 19B. Disadvantageously, however, irrespective of which gas injection port or orifice, or combination of gas injection ports or orifices, is utilized, a gas pressure gradient will exist from the top to the bottom of chamber 11, and in addition, a difference in gas pressure across the sides of substrate 4 will be established if the pumping path for gas evacuation is not symmetrical.
The top-to-bottom process gas pressure gradient which is established as described above typically has an adverse affect on the properties of the sputter deposited thin films. More specifically, the top-to-bottom gas pressure gradient results in circumferentially non-uniform magnetic properties of the various magnetic layers, including soft underlayers and longitudinal and perpendicular recording layers. The effect of circumferential non-uniformity of the sputter deposition process is particularly observed when the films are formed by a reactive sputtering process, as in the formation of granular magnetic films.
Another apparatus for performing cathode sputter deposition of thin films on circular disk-shaped substrates with circumferential uniformity comprises a circularly-shaped planar magnetron sputtering source with a rotating magnet assembly provided adjacent the back side surface of the sputtering target for increasing uniformity of sputtering therefrom and increasing target lifetime. The sputtering source comprises a circular disk-shaped cathode/target with a planar sputtering surface provided with a ring-shaped gas channel extending around the circumference thereof, with the front facing side or surface of the gas channel provided with a plurality of substantially equally spaced small gas injection holes or orifices (e.g., of 0.025″ diameter) for uniform injection of process gas into the sputtering chamber between the target and the disk-shaped substrate. The gas channel is provided with gas from a source via a relatively larger gas inlet opening formed on the rearward facing surface thereof.
According to the design principle of this apparatus, the injection holes or orifices of the gas channel must be sufficiently small in order to ensure an even gas distribution around the target. In general, the smaller the holes or orifices, the better the gas distribution. However, if the holes or orifices are too large, the process gas(es) enter the sputtering chamber via the holes or orifices nearer the gas inlet. Nonetheless, other issues are generated when the holes or orifices are too small. For example, when the holes or orifices are too small, an excessively long interval is required for pressurizing the sputtering chamber, thereby reducing the product throughput. In addition, the interval required for evacuating process gas(es) from the chamber is disadvantageously lengthened, the effect of slow pump-out being heightened when reactive gases, such as O2, must be removed from the chamber, for example, in order not to contaminate neighboring chambers of a multi-chamber sputtering apparatus utilized for automated manufacture of magnetic and MO recording media.
A sputter deposition apparatus has previously been disclosed with a gas supply system adapted for providing the process (i.e., vacuum) chamber of the apparatus with a uniform flow of at least one process gas around the entirety of a circumferentially extending edge of a cathode sputtering source in the form of a circularly-shaped planar magnetron sputtering target assembly with a fixed (i.e., static) magnetron magnet assembly, wherein the gas supply system comprises a gas inlet conduit adapted for introducing the at least one process gas into a space formed between a rear side of the sputtering target assembly and a mounting plate for mounting the sputtering source to a wall of the process chamber. The gas supply system further comprises a gap formed between the circumferentially extending edge of the sputtering target assembly and a cathode dark space shield surrounding the edge, the space and the gap being in fluid communication.
However, in the case of circularly-shaped planar magnetron target assemblies comprising rotating magnetron magnet assemblies for enhanced uniformity of sputtered particle distribution and target erosion (hence increased lifetime), the aforementioned gap (between a heat sink of the target and the magnet assembly) is extremely small, rendering back-side process gas injection (as described above) difficult or impractical. More specifically, while the spacing between the heat sink and the magnet assembly is adjustable in some available models of rotating magnetron target assemblies, the magnet assemblies must be positioned very closely to the target (or its heat sink) in order to strike a satisfactory sputtering plasma with low pass-through flux (“PTF”) target materials, such as utilized for depositing magnetic recording layers and magnetically soft underlayers (“SUL”s).
In view of the foregoing, there exists a clear need for improved means and methodology for depositing thin films by sputtering techniques (e.g., reactive sputtering) utilizing magnetron sputtering sources with rotating magnets and at deposition rates consistent with the throughput requirements of automated manufacturing processing, which have a specified, typically minimal, variation of composition and/or properties over the substrate surface. More specifically, there exists a need for improved means and methodology for overcoming the above-described drawbacks and disadvantages associated with rotating magnet sputter deposition processing for the manufacture of hard disk magnetic and MO recording media, notably reactive sputtering involving oxide content variation over the disk surface which exceeds specified manufacturing tolerances.
The present invention addresses and solves the problems, disadvantages, and drawbacks described supra in connection with conventional means and methodology for performing sputter deposition of thin films, particularly reactive sputtering of oxide-containing perpendicular magnetic recording layers, while maintaining full compatibility with all aspects of conventional automated manufacturing technology for hard disk magnetic and MO recording media. Further, the means and methodology afforded by the present invention enjoy diverse utility in the manufacture of all manner of devices and products requiring formation of high compositional uniformity thin films by means of reactive sputtering processing.